1. Field of the Invention
The present invention relates to vibration-reducing apparatuses constituted by moving masses that are resiliently suspended and displaced by electromagnetic motors in directions opposite to those of the vibrations to be reduced, with the electromagnetic motors being servo-controlled to the vibration that is to be reduced in such a manner as to cause it to be decreased by a previously-set amount.
The invention is applicable whenever vibration reduction is a strategic or an economic need: military hardware, land or sea vehicles, civil aircraft, or in general wherever the presence of vibration is detrimental.
A usual disposition is shown diagrammatically in FIGS. 1A and 1B, FIG. 1B being an enlarged section view of a proton of FIG. 1A. The moving mass (1) is suspended on springs (2). The electrodynamic motor is constituted by a coil (3) carrying an alternating current that is an image of the displacement of the frame, and a magnet (4) providing a magnetic field in an air gap (5). The moving mass (1) is thus driven in the same manner as a loudspeaker membrane.
A regulator (6) and an amplifier (7) deliver control current to the coil (3) determined as a function of the vibratory amplitudes measured by an accelerometer (8) placed on the structure of the machine (9).
If m is the mass of the machine and v is its velocity prior to application of the apparatus, and M and V are the mass of the moving mass (1) and its vibratory velocity, then M.V-m.v=0 when the vibratory speed of the machine is cancelled.
When used under real conditions, the usual disposition of FIG. 1 suffers from the drawback of being heavy and bulky, since in order to reduce the propagation of vibration from a machine to the environment, it is necessary to reduce all six mechanical components of vibration at a point, which components are as follows (FIG. 2):
three vibratory velocities along three axes Ox, Oy, and Oz; and PA1 three moments of rotation about the three axes Ox, Oy, and Oz. PA1 on adopting motion for the active masses that is planar or tri-axial; and PA1 on a plurality of motors constituted by electromagnets of effectiveness and endurance that are well known.
Thus, in order to obtain significant reduction of vibration, six devices are required, located as shown by way of example in FIG. 3. The amplifiers, regulators, and accompanying circuits, together with the measuring accelerometers are not shown: only the six apparatuses are shown.
Another drawback of those apparatuses results from the difficulty of evacuating the heat generated by the current flowing through the coil (3) of FIG. 1 which is thermally isolated from the structure, since the support (10) of FIG. 1 is necessarily constituted by a material that does not conduct electricity and that Is therefore a poor conductor of heat, thereby impeding the flow of heat to other, cooler locations.
To mitigate that drawback which reduces the lifetime of that type of apparatus, due in particular to the thermal and mechanical aging of the electrical insulators, it is often necessary to add a cooling fan whose own operation serves to generate vibrations in addition to the amplitudes that are to be reduced, or indeed to add cooling systems that rely on a flow of liquid coolant.
That limitation prevents the above disposition operating in high temperature applications.
Finally, a last drawback comes from the fact that the active mass is often suspended on annular springs commonly called "speeders", having a lifetime that is short and uncertain. In addition to the drawback of lifetime that is limited or uncertain since it is difficult to calculate, the above configuration is bulky, voluminous, and heavy.
Those drawbacks mean that apparatuses of the above type or variants thereof are used very little in industry and are intended more for laboratory testing.
That old design is constrained by the linear relationship that exists between the control current and the force generated, which disposition is unavoidable when servo-control is based on analog electronics.
The linearity constraint has now disappeared with the arrival of regulators and control devices that are digital.